(1) Short for Post Office Protocol, a protocol used to retrieve e-mail from a mail server. Most e-mail applications (sometimes called an e-mail client) use the POP protocol, although some can use the newer IMAP (Internet Message Access Protocol).
There are two versions of POP. The first, called POP2, became a standard in the mid-80's and requires SMTP to send messages. The newer version, POP3, can be used with or without SMTP.
(2) Short for point of presence, an access point to the Internet. ISPs have typically multiple POPs. A point of presence is a physical location, either part of the facilities of a telecommunications provider that the ISP rents or a separate location from the telecommunications provider, that houses servers, routers, ATM switches and digital/analog call aggregators.
(3) Short for Programmed Operator (POP), a
pseudo-opcode in a virtual machine language executed
by an interpretive program. The Programmed Operator instructions provide the
ability to define an instruction set for
efficient encoding by calling subprograms into primary
memory.
(4) Short for picture-outside-picture
POP is a feature found on some televisions that allows the user to divide the
screen into two same-size pictures, enabling you to view a second program.
Compare with picture-in-picture (PIP).
